Whisk the cocoa powder, confectioners' sugar and milk in the top of a double boiler over boiling water until smooth. Add the chocolate chips and stir until the chips are melted. Stir and lower the heat to simmer. In a large bowl, beat the egg whites until soft peaks form. Gradually add sugar and beat until stiff peaks form. Fold the vanilla and 1/2 cup chocolate mixture into the egg white mixture. Bring the water in the bottom of the double boiler back to a boil. Stir the chocolate-egg white mixture into the chocolate mixture in the top of the double-boiler. Using an electric beater or a whisk, beat this mixture for a minute or until it is well combined. Cover the double boiler and continue to cook over boiling water for 25-30 minutes or until the souffle is puffed and set. Serve with lowfat whipped topping, if desired.